Jet fuel starter engines (also called gas turbine starters) are generally designed and built robustly and safely. Jet fuel starters are generally comprised of multiple components that fit together to comply with certain clearances for optimal engine performance. Additionally, these well-designed engines may need to undergo periodic maintenance and/or repair. Such maintenance and repair operations may include partial or complete disassembly of the engine, and removal, repair, or replacement, of one or more components within the engine. Some of the components may be installed in the engine according to relatively tight tolerances. Although these same components may be manufactured to within design specification tolerances, manufacturing variations may still exist. Thus, engine production and engine re-assembly following maintenance and/or repair may include instances in which these variations are accounted for by using, for example, mechanical shims.
For example, in a jet fuel starter engine, it is desirable that the axial clearance between the compressor impeller and the shroud, which surrounds a portion of the impeller, meets a predetermined desired clearance for efficient impeller operation. When an impeller rotates for a duration of time, kinetic energy from the rotation produces heat. Most preferably, the clearance between the impeller and shroud allows the heat to properly dissipate, which may result in a more efficiently run engine. Conversely, as this axial clearance increases, engine efficiency may decrease. To obtain the appropriate clearance during manufacture or following maintenance or repair, the clearance between the impeller vanes and shroud may be manually positioned, and a measurement gauge may be used to check the clearance between the impeller vanes and the shroud. The impeller and shroud may be manually adjusted and mechanical shims may then be fitted between the shroud and another portion of the engine to obtain the appropriate clearance.
The above-described method of manual positioning, measuring, and adjusting the impeller to the appropriate clearance is generally safe and reliable. However, it may present certain drawbacks. For example, the method by which the impeller is positioned may not be accurate and/or may be time-consuming. Additionally, the method may lack repeatability, thus, the clearance height of each impeller may vary. As a result, the impeller and/or shroud components may be marred or damaged due to improper positioning causing the affected components to be discarded. Moreover, inappropriate positioning may lead to shaft imbalance and improper clearance when the engine is placed back into operation. If there is too little clearance, this decreased clearance may result in less than optimum engine performance and, in some cases, may result in the impeller physically contacting the shroud.
Therefore, there is a need for an apparatus and method that addresses one or more of the above-noted drawbacks. Namely, an apparatus and method that provides accurate readings of the distance between an impeller and shroud so that accurate placement of the impeller within a jet fuel starter engine may be achieved. Moreover, it is desirable to have a tool that assists in the proper adjustment of clearances between the impeller and other components within the engine. The present invention addresses one or more of these needs.